Internal combustion engines may utilize a supercharger or turbocharger to compress ambient air entering the engine in order to increase power. Further, engines may recirculate a portion of exhaust gas from the exhaust line to upstream of a compressor of the supercharger at increasing rates to decrease NOx emissions. At high exhaust-gas recirculation rates, the fraction of gaseous components in the charge air increase. When a temperature of the charge air, a mixture of ambient air and recirculated exhaust gas, falls below a dew point temperature, condensate may form in the compressor and/or intake line. Condensate formation may lead to compressor wheel damage and/or irreversible damage of components downstream of the compressor.
One example method to avoid condensate formation is shown by Eitel et al in EP 1724453. Therein, a two stage exhaust gas cooler is placed on the exhaust gas recirculation (EGR) line, in order to lower the temperature below a components dew point, followed by a condensate trap in order to remove unwanted components in the exhaust gas. The exhaust gas is then mixed with the intake air, after condensate removal, downstream the compressor. Another example method is shown by Raunio in EP 2513449. A high temperature cooling circuit and a low temperature cooling circuit are used to cool intake air. The system uses multiple heat exchangers in series and includes one junction to provide high temperature cooling liquid to the low temperature cooling circuit heat exchanger located upstream of the compressors.
However, the inventors herein have recognized potential issues with such systems. As one example, lowering the temperature of the EGR line does not account for condensate formation which may occur in the intake line, leading to condensate formation which may irreversibly damage system components. In another example, utilizing multiple heat exchangers leads to increased costs and system complexity.
The inventors herein have recognized the above issues and developed a supercharged internal combustion engine comprising at least one intake line, arranged in an intake system, for supplying charge air to the internal combustion engine. At least one compressor, arranged in the intake line, comprises at least one rotor mounted on a rotatable shaft and a housing in which said at least one rotor is arranged, wherein the housing has at least one integrated coolant duct and is equipped with a liquid-type cooling arrangement. Further, an at least one exhaust line, arranged in an exhaust gas discharge system, is provided for discharging exhaust gases, wherein an exhaust-gas recirculation arrangement, the recirculation line of which branches off from the exhaust-gas discharge system and issues into the intake system upstream the compressor is included. The system forms a liquid-type cooling arrangement, wherein a cooling circuit is provided through the at least one coolant duct integrated in the housing, and wherein a heat exchanger is arranged in the cooling circuit upstream of the housing, which heat exchanger serves for heating the cooling liquid, and the at least one compressor is a constituent part of an exhaust-gas turbocharger.
As an example, the heat exchanger may be coupled to a heated coolant to transfer heat from the heated coolant to the cooling liquid. The heated cooling liquid may then be passed directly from the heat exchanger to the intake compressor housing coolant duct in order to heat the charge air to reduce condensation formation. Further, the coolant flow through the heat exchanger may be adjusted responsive to the charge air temperature being over a threshold via switching a shut-off valve positioned in a bypass line branching upstream of a heat exchanger and re-joining downstream the heat exchanger and upstream the intake compressor housing. In one example, switching the shut-off valve to a closed position, when the charge air temperature is below a dew point temperature, allows coolant flow through the heat exchanger and blocks coolant flow through the bypass. In another example, switching the shut-off valve to an open position allows coolant flow through the bypass line and blocks coolant flow through the heat exchanger, when a charge air temperature is above a first threshold. The cooling liquid temperature may then be adjusted to reduce condensation and allow high exhaust-gas recirculation rates.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.